The present invention relates to a loading device having a loading arm movable in the vertical direction.
Loading devices having swingable loading arms movable in the vertical direction are generally so constituted that a loading arm takes up a workpiece from a workpiece supplying spot by a pick-up mechanism disposed on the end portion of the arm, then the loading arm swings through a predetermined angle and sets the workpiece on a loading spot.
Therefore, using such a loading device of swing type, especially for loading a small workpiece, the fixing of the workpiece supplying location and the loading location requires a higher degree of accuracy. For ensuring higher position fixing accuracy, the loading arm is commonly located at the swivel ends thereof in such a manner that a stopper on the arm swings into contact with a second stopper secured on the base frame to thereby accurately fix the end positions.
The position fixing of this fixed-stopper-contact method is indeed more excellent in accuracy, lasting quality and reliability than that of using either a cam mechanism or electroservo mechanism.
But, in this position fixing method, the loading arm moves vertically just at a located swivel position thereof so that pressure contact between the pair of coacting stoppers, one being on the loading arm and the other on the fixed base frame must be maintained during the vertical movement of the arm. That is, while the loading arm moves vertically, the stopper on the arm is rubbing along the stopper face of the base frame with some friction. Accordingly, the loading arm needs a strong force for its vertical movement and therefore is unable to move smoothly and speedily. In addition, it is inevitable for the stoppers to be worn away, so that good maintenance of the locating accuracy could not be expected.
Furthermore, in the automatic loading of plate-like workpieces one by one on a die of a press machine, if two or more workpieces are loaded in piles due to a misoperation of the loading device, the pressing operation exerts an overload upon the press machine which can damage the die set. Similarly, if the die set is not occupied by a workpiece during the pressing operation, the die set is apt to be damaged and its life shortened.
Therefore, it is usual in automatic loading devices for press machines to provide a work disorder loading detector to detect and discriminate normal work placing from abnormal and to stop the press machine when an abnormal loading is detected.
A photo-electric detector used in the prior art detects whether work loading is in proper condition or not, but such a detector can not detect loaded works in piles. An air-jet sensor also detects only whether the work is spaced on the die or not. All of the conventional detectors can not detect when the work is in disorder on the die.